LOGAN, Utah — In most states, if somebody is texting behind the wheel and causes a crash that injures or kills someone, the penalty can be as light as a fine.

Utah is much tougher.

After a crash here that killed two scientists — and prompted a dogged investigation by a police officer and local victim’s advocate — Utah passed the nation’s toughest law to crack down on texting behind the wheel. Offenders now face up to 15 years in prison.

The new law, which took effect in May, penalizes a texting driver who causes a fatality as harshly as a drunken driver who kills someone. In effect, a crash caused by such a multitasking motorist is no longer considered an “accident” like one caused by a driver who, say, runs into another car because he nodded off at the wheel. Instead, such a crash would now be considered inherently reckless.

“It’s a willful act,” said Lyle Hillyard, a Republican state senator and a big supporter of the new measure. “If you choose to drink and drive or if you choose to text and drive, you’re assuming the same risk.”

The Utah law represents a concrete new response in an evolving debate among legislators around the country about how to reduce the widespread practice of multitasking behind the wheel — a topic to be discussed at a national conference about the dangers of distracted driving that is being organized by the Transportation Department for this fall.

Studies show that talking on a cellphone while driving is as risky as driving with a .08 blood alcohol level — generally the standard for drunken driving — and that the risk of driving while texting is at least twice that dangerous. Research also shows that many people are aware that the behavior is risky, but they assume others are the problem.

Treating texting behind the wheel like drunken driving raises complex legal questions. Drunken drivers can be identified using a Breathalyzer. But there is no immediate test for driving while texting; such drivers could deny they were doing so, or claim to have been dialing a phone number. (Many legislators have thus far made a distinction between texting and dialing, though researchers say dialing creates many of the same risks.)

If an officer or prosecutor wants to confiscate a phone or phone records to determine whether a driver was texting at the time of the crash, such efforts can be thwarted by search-and-seizure and privacy defenses, lawyers said.

Prosecutors and judges in other states already have the latitude to use more general reckless-driving laws to penalize multitasking drivers who cause injury and death. In California, for instance, where texting while driving is banned but the only deterrent is a $20 fine, a driver in April received a six-year prison sentence for gross vehicular manslaughter when, speeding and texting, she slammed into a line of cars waiting at a construction zone, killing another driver.

But if those prosecutors want to charge a texting driver with recklessness, they must prove the driver knew of the risks before sending texts from behind the wheel.

In Utah, the law now assumes people understand the risks.

The law “is very noteworthy,” said Anne Teigen, a policy specialist with the National Conference of State Legislatures, an organization of state legislators. “They have raised the bar and said texting while driving is not just irresponsible, and it’s not just a bad idea — it is negligent.”

Ms. Teigen said legislators throughout the country were struggling with how to address threats created by new technology, just as they once debated how to handle drunken driving.

Ray LaHood, the transportation secretary, has said drivers should not text behind the wheel, and several United States senators recently introduced legislation to force states to ban texting while driving.

Utah, governed by a Republican legislature with a libertarian bent, may seem an unlikely state to pursue particularly tough penalties governing driver behavior.

But the issue forced itself onto the legislative agenda here because of what occurred on the rainy morning of Sept. 22, 2006.

The accident occurred on a two-lane highway just west of Logan, in a verdant valley in Utah’s northernmost county.

Reggie Shaw, a 19-year-old college student working as a house painter, was driving west to work in a Chevrolet Tahoe S.U.V. Approaching him, in a Saturn sedan, was James Furaro, 38, and his passenger, Keith P. O’Dell, 50. The senior scientists were commuting to ATK Launch Systems, where they were helping to design and build rocket boosters.

Mr. Shaw crossed the yellow dividing line on the two-lane road and clipped the Saturn. It spun across the highway and was struck by a pickup truck hauling a trailer filled with two tons of horseshoes and related equipment.

The two scientists were killed instantly.

At the scene, the investigating officer, Bart Rindlisbacher of the Utah Highway Patrol, said he could not pinpoint the cause of the crash. Mr. Shaw said he could not remember doing anything out of the ordinary.

The trooper figured it was an unfortunate case of “left of center,” a catch-all for a traffic offense that involves crossing the yellow divider.

But a witness told the police he had seen Mr. Shaw swerving several times just before the accident, raising Mr. Rindlisbacher’s suspicions. The trooper’s concerns grew as he drove Mr. Shaw to the hospital. He saw Mr. Shaw, in the passenger seat, pull out his phone and start texting.

“Were you texting while you were driving?” Mr. Rindlisbacher recalled asking.

“No,” he recalled Mr. Shaw responding. (Mr. Shaw said he did not remember the conversation or much about the accident.)

The trooper was deeply skeptical. He figured out how to subpoena Mr. Shaw’s phone records. Six months later, with help from a state public safety investigator, they got the records and their proof: Mr. Shaw and his girlfriend had sent 11 text messages to each other in the 30 minutes before the crash, the last one at 6:47 a.m., a minute before Mr. Shaw called 911. Investigators concluded he sent that last text when he crossed the yellow line.

Still, county prosecutors thought they were unable to charge Mr. Shaw with something other than “left of center.” For instance, if they wanted to prove Mr. Shaw guilty of negligent homicide, a misdemeanor, they would need to show he knew of the dangers or should have known of the dangers of texting while driving.

Mr. Shaw, who had retained a lawyer, would not discuss the issue with law enforcement or prosecutors.

Then Terryl Warner, a victim’s advocate in the county where the accident occurred, got involved.

Ms. Warner had a personal interest in the case because she knew the family of one of the scientists.

In July 2007, Ms. Warner, convinced by the trooper’s evidence, wrote to prosecutors arguing for a vehicular manslaughter charge. She said the dangers of texting and driving were broadly known, therefore Mr. Shaw should have known better.

Mr. Shaw had just started a Mormon mission in Canada when he was called home to face charges of negligent homicide. The trial was set for early 2009.

Then, just before Thanksgiving in 2008, at a hearing, Mr. Shaw looked at the families of the two dead scientists and decided he could no longer keep dismissing the phone records that showed he was texting, even though his lawyers advised him to remain quiet. “It hit me that I was being selfish dragging this on,” he said. “I decided I’ve got to do whatever it takes to make this come to an end. If there was anything I could do — spend a year in jail, two years in jail, whatever — I’d do it.”

He pleaded guilty to two counts of negligent homicide, but his record will be cleared if he fulfills the sentence imposed by the judge. It included 30 days in jail, 200 hours of community service, and a requirement that he read “Les Misérables” to learn, like the book’s character Jean Valjean, how to make a contribution to society.

Last February, Mr. Shaw spoke to the state House Subcommittee on Law Enforcement and Criminal Justice, which was considering a ban on texting for motorists. The measure seemed likely to fail given the legislature’s lack of interest in previous such efforts. Then Mr. Shaw stood to talk about his crash and started sobbing.

“I was the one driving and texting,” Mr. Shaw said through tears. “Excuse me. I apologize. I didn’t know the dangers.”

Ms. Warner, the victim’s advocate, said that moment was a turning point. “Before he spoke, some legislators were talking and texting,” she recalled. “After he started talking, there wasn’t a dry eye in the room.”

Under Utah’s law, someone caught texting and driving now faces up to three months in jail and up to a $750 fine, a misdemeanor. If they cause injury or death, the punishment can grow to a felony and up to a $10,000 fine and 15 years in prison.

Alaska is the only other state that takes a similarly tough approach to electronic distraction, said Ms. Teigen of the National Conference of State Legislators.

A law passed there in 2007 makes it a felony punishable by up to 20 years in prison if a driver causes a fatal accident when a television, video monitor or computer is on inside the car and in the driver’s field of vision. (The law applies to phones used for texting, but not to phones used exclusively for calling or to some other devices, like GPS devices.)

The law, which is less focused on texting than Utah’s, resulted from a 2003 accident in which a driver, who prosecutors said was watching a movie on a video monitor perched on his dashboard, killed two motorists.

These tougher penalties can lead to prickly legal questions.

John Wesley Hall, who just stepped down as president of the National Association of Criminal Defense Lawyers, said the police might have difficulty proving a driver suspected of texting wasn’t merely dialing a phone. And, he said, there are serious privacy and search issues raised when an officer wants to confiscate a phone.

“The police have no business going into my phone,” he said.

James Swink, the Cache County attorney, expects such challenges, but says that the police in some cases could simply get phone records later, as in the Shaw case.

More broadly, Mr. Swink said, drivers in Utah are now on notice that texting while driving is inherently reckless. And as drivers across the nation become more aware of that notion, he said, judges and prosecutors will feel more comfortable asking for big penalties. He said the Shaw case helped to pave the way.

“Once the word is out there,” he said, “it will become easier for judges to lower the big boom.”